Effects of Ionizing Radiation in Cocrystals of DNA Model Compounds: ESR-ENDOR Studies of X-Irradiated Imidazole:Barbital and Adenosine:5-Bromouracil

摘要

Electron spin resonance (ESR) and electron nuclear double resonance (ENDOR) techniques have been used to study radition induced damage in cocrystalline complexes. The study addresses the following questions: (1) whether radiation induced damage is stabilized preferentially on one of the components of the cocrystalline system; and (2) whether charge transfer occurs between purine and pyrimidine bases in hydrogen bonded or stacked configurations. The cocrystals used are imidazole: 5,5-diethylbarbituric acid (barbital) and adenosine: 5-bromouracil (AR:BU). The predominant free radicals trapped in single crystals of this complex X-irradiated at 12K are the barbital pi -anion and the imidazole pi -cation. Structural analysis of the imidazole ring relative to the crystal structure at 300K. The preferential stabilization of pi -anions on barbital and pi -cations on imidazole is explained by a selective electron capture model. The radiation chemistry of the AR:BU cocrystal at 12K shows that electron gain and electron loss products are stabilized on both A and BU. These results indicate that (1) preferential stabilization of radition damage may be observed in a cocrystal even in the absence of stacking interactions; (2) in the presence of purine:pyrimidine stacking electron transfer may occur, but hole transfer is not likely to be the mechanism of redistribution of radiation damage in cocrystalline systems. The radiation chemistry of AR:BU is used as a model to predict the effects of ionizing radiation on DNA. 22 figures, 8 tables. (ERA citation 09:044068)